1. Field of the Invention
The present invention generally relates to an inkjet recording apparatus and method and, more particularly, to an inkjet recording apparatus and method for recording an image on a recording medium by an interlace printing method.
2. Description of the Related Art
Inkjet recording apparatuses are used in various image-forming apparatuses such as a printer, a facsimile machine or a copy machine. There are several types of inkjet recording apparatuses such as a serial scanning type inkjet recording apparatus or a line type inkjet recording apparatus.
The line type inkjet recording apparatus records an image by using a recording head having a length corresponding to the entire length of a main scanning area. That is, the recording head is provided with a plurality of nozzles arranged in an extending direction of the recording head which corresponds to a main scanning direction so that the nozzles cover the entire width of a recording medium such as a recording paper on which an image is formed. According to the line type inkjet recording apparatus, an image is recorded on the recording medium by projecting ink drops onto the recording medium by moving the recording medium in a direction perpendicular to the extending direction of the recording head.
The serial scanning type inkjet recording apparatus records an image by using a recording head having a plurality of nozzles arranged in a sub-scanning direction. An image is recorded on a recording medium such as a recording paper by projecting ink drops onto the recording medium by moving the recording head in a main scanning direction while the recording medium is stepwisely moved in a sub-scanning direction.
In the above-mentioned inkjet recording apparatuses, recording density (dot density) is determined by a pitch of the nozzles provided on the recording head. Accordingly, in order to achieve a high-density recording, the pitch of the nozzles must be decreased. However, there is a limit in the pitch size due to difficulty in formation of the nozzles with a small pitch. Thus, there is a limit in increasing the recording density.
As a conventional inkjet recording apparatus, Japanese Patent Publication No.3-56186 discloses an inkjet recording apparatus which uses an interlace printing method in which a main scanning is performed k times while a recording head moves a single pitch D of nozzles arranged on the recording head in a sub-scanning direction so as to record an image with a dot density smaller than the pitch D of the nozzles in the sub-scanning direction. Additionally, Japanese Patent No.2613205 discloses an inkjet recording apparatus which has a recording head provided with N nozzles and performs a main scanning operation and a sub-scanning operation with a dot pitch P alternately n times, and, thereafter, a sub-scanning is performed with a pitch corresponding to P{n(N-1)+1}.
Additionally, Japanese Laid-Open Patent Application No.7-242025 discloses an inkjet recording apparatus which eliminates a non-recordable area generated when an image is recorded by an interlace printing method such as that used in the inkjet recording apparatus disclosed in the above-mentioned Japanese Patent Publication No.3-56186.
Further, Japanese Laid-Open Patent Application No.5-155040 discloses an inkjet recording apparatus which generates an irregular thin-out pattern in a template buffer by utilizing a random numbers each time a recording operation corresponding to a single scanning is performed so that a lower half of data corresponding to a single scanning operation and an upper half of data corresponding to a subsequent scanning operation are thinned out in accordance with the thin-out pattern.
However, in the above-mentioned conventional inkjet recording apparatuses which use an interlace printing method in which a plurality of main-scanning operations are performed while the recording head travels a distance corresponding to a pitch of the nozzles, an unevenness in density of a recorded image is generated in an area between a part of the recorded image by a train of nozzles and a subsequent part of the recorded image since a travel of a recording head in a sub-scanning direction fluctuates due to variation in a thickness of a recording medium on which the image is recorded or an eccentricity of a roller for feeding the recording medium. The unevenness in image density is generally referred to as a band which is periodically appears in each area between series of scanning operations in a sub-scanning direction.
Additionally, in the inkjet recording apparatus using a template buffer, there is a problem in that a large memory is required since the buffer must store data corresponding to a whole scanning operation.